•Relation between drag reduction and viscoelasticity of polymers is investigated.•Drag reduction correlates with extensional viscosity and Weissenberg number.•Drag reduction does not correlated with ...small-amplitude oscillatory shear.•For large degradation, extensional viscosity increases with decreasing strain rate.
The relation between the drag reduction (DR) performance of several water-soluble polymers and their viscoelastic properties was investigated. Polymers with a flexible molecular structure including three grades of polyacrylamides (PAM), and a polyethylene oxide (PEO) were investigated. Xanthan gum (XG) and carboxymethyl cellulose (CMC), each with a rigid molecular structure, were also considered. The rheology was characterized using steady shear-viscosity measurement, capillary break-up extensional rheometer (CaBER), and small-amplitude oscillatory shear measurement at the concentration of the drag-reduced solution. To isolate the effect of shear viscosity, the concentration of the polymers was adjusted to produce solutions with a similar shear viscosity at high shear rates. Using pressure drop measurements in a turbulent pipe flow, the DR of each polymer solution was determined. With identical high-shear-rate viscosities, the flexible PAM solutions resulted in an initial DR of 50–58%, while the initial DR of PEO was 44%, and the rigid polymers provided the least DR of 12%. The rigid polymers demonstrated negligible degradation of DR over a period of 2 h. Of the flexible polymers, PAM showed moderate degradation, while the DR of PEO quickly diminished after 20 min. Drag reduction correlated with extensional viscosity and Weissenberg number obtained from CaBER. A strong correlation was not observed between DR and the viscoelastic moduli obtained from small-amplitude oscillatory shear. The large mechanical degradation of PEO was associated with a continuous extensional thickening, in which extensional viscosity increased with decreasing strain rate until the filament broke up.
A significant fraction of the experimental works on the rheology of polymer melts include an attempt to find the zero‐shear‐rate viscosity η0. This is done for good reasons, because η0 is a limiting ...property that depends only on thermodynamic variables and, importantly, the molecular and supermolecular structure of the melt. As with all limiting properties, η0 is impossible to measure directly. Fortunately with many melts, it can be estimated from viscosity measurements at very low shear rates or frequencies, but still remains one of those properties that becomes in the limit very prone to error. The common approach is to use a set of frequency‐ or shear‐rate‐dependent data and extrapolate to find η0. As with any extrapolation, the major question is the function used for the extrapolation. This question is addressed in some detail in this article. The question of which function to use was discarded in favor of using a large sample of 20 equations of many functional forms. This sample of randomly chosen equations was used to generate a set of η0 values, and the statistics of this distribution were examined, in the usual fashion, by description with an analytical probability density function that gives a high probability of being a likely generator of the data. In addition, a weighted average was proposed, where the weighting factor takes into account the quality of the fit. For testing these ideas, the room temperature melts of poly(vinyl isobutyl ether), poly(isobutylene), and poly(dimethyl siloxane) were used. The η0 of the latter was reachable; for the other resins, a falling ball technique was attempted.
The zero‐shear‐rate viscosity, η0, is a limiting material property that depends on thermodynamic variables and composition of a polymer. As with all limiting properties, η0 is impossible to measure directly. It can be estimated from viscosity measurements at very low shear rates or frequencies, but becomes in the limit very prone to error. The common approach is to extrapolate frequency‐ or shear‐rate‐dependent data to find η0. The major question is the function used for the extrapolation; this is addressed in some detail in this article, but was discarded in favor of using a sample of 20 equations of many functional forms. These randomly chosen equations were used to generate a set of η0 values, and the statistics of this distribution were examined, in the usual fashion, by description with an analytical probability density function that gives a high probability of being a likely generator of the data. In addition, a weighted average was proposed, where the weighting factor takes into account the quality of the fit. For testing these ideas, the room temperature melts of poly(vinyl isobutyl ether), poly(isobutylene), and poly(dimethyl siloxane) were used. The η0 of the latter was reachable; for the other resins, a falling ball technique was attempted.
In this paper, viscosity of SAE 5W50 oil enriched by MWCNT and ZnO nanoparticles with combination ratio of 1:4 is experimentally investigated in solid volume fractions of 0.05, 0.1, 0.25, 0.5, 0.75, ...and 1% and temperature range of 5 to 55 ˚C. It is done with the aim of feasibility study on achieving a modified nano-engine oil that can minimize cold start engine damages using nanoparticles. According to results, produced nano oil with concentrations less than 0.25% selected as modified engine oil. Almost 9% reduction in viscosity of nano-oil with solid volume fraction of 0.05% compared to ordinary engine oil in 5 °C and shear rate of 666.5 (1/sec) was one of the very interesting results of this investigation which makes pumping easier and oil will enter the lubrication cycle faster and this minimizes cold start damages. Moreover, Presence of nanoparticles improves heat transfer from engine parts. The result showed that in temperature range of 35–55 °C, and solid volume fractions less than 0.25%, our proposed nano-oil is more appropriate for high temperature usage too, because of lower dependency of its viscosity to temperature in comparison to pure 5W50 engine oil. A mathematical correlation was proposed to predict viscosity of nano-engine oils used in this research. R-Squared = 0.9685 of this correlation shows its high accuracy.
•Proposing new nano-engine oil with the aim of lowering cold start engine damages.•Viscosity reduction at solid volume fractions less than 0.25%.•Feasibility study of using MWCNT-ZnO(20%–80%)/5W50 for EOR applications.
Hybrid nanofluids are gaining a wide range of applications due to their reported improvement in heat transfer properties. This study presents an experimental investigation into the specific heat and ...viscosity of Al2O3-ZnO water hybrid nanofluids at three mixture ratios. The specific heat and viscosity measurements are taken over different temperatures at different volume concentrations. The study compared the experimental data to classical models and observed that the specific heat model overestimated and the viscosity model underestimated experimental obtained values. According to results, the particles mixture ratio has a significant effect on both specific heat and viscosity of the hybrid nanofluids. Viscosity increases while specific heat decreases by increasing the volume concentration. Al2O3-ZnO water hybrid nanofluids at 2:1 mixture ratio have a maximum viscosity increase of 96.37% and maximum specific heat decrease of 30.12% at a temperature of 25 °C and volume concentration 1.67%.
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•The specific heat and viscosity of Al2O3-ZnO dispersed in water is investigated.•Al2O3-ZnO water nanofluids at 2:1 mixture ratio have a maximum viscosity increase of 96.37%.•Maximum specific heat decrease of the Al2O3-ZnO water nanofluids was 30.12%.•Al2O3-ZnO hybrid nanofluid at 1:1 mixture ratio is most ideal for heat transfer application.•Theoretical models do not account for the effect of mixture ratio in the nanofluid.
We examine the mean relaxation time predicted by the Maxwell relation for stress and structural α‐relaxation phenomena. We express this relation using the Markov network framework and present an ...expression for the average relaxation time under equilibrium and nonequilibrium conditions that is rooted in the energy landscape of a material. We show that structural relaxation times calculated using the Maxwell relation must systematically underpredict the relaxation time. Finally, we report experimental evidence suggesting that the relaxation time obtained from shear viscosity measurements must correspond to a stress relaxation time.
The 3D Lagrangian residual velocity (LRV) is solved analytically in a narrow bay employing a vertically varying eddy viscosity coefficient. The nondimensional vertical profile of the eddy viscosity ...is described by a parabola that is characterized by its minimum value and the location of its symmetry axis. The results show that the LRV has similar structures as that under constant eddy viscosity coefficient when the magnitude is the same. The tidal body force that drives the residual velocity contains two terms, the advection and Stokes’ drift. The total LRV, as well as the LRV induced by each term, are very sensitive to the magnitude of the eddy viscosity coefficient, while the specific profile matters less. With a given magnitude, the specific profile of the varying eddy viscosity coefficient affects the total LRV by changing the LRV induced by the advection term. Moreover, the contribution mechanism of each component of the tidal body force to the total LRV is analyzed. The 3D LRV is mainly determined by the Stokes’ drift stress term regardless of the steepness of the across-bay topography. The depth-integrated and breadth-averaged LRV are mainly determined by the Stokes’ drift stress term with steep topography, but the Stokes’ drift contribution is no longer obvious with gentle topography.
We present the first comprehensive study of r-process element nucleosynthesis in the ejecta of compact binary mergers (CBMs) and their relic black hole (BH)–torus systems. The evolution of the ...BH–accretion tori is simulated for seconds with a Newtonian hydrodynamics code including viscosity effects, pseudo-Newtonian gravity for rotating BHs, and an energy-dependent two-moment closure scheme for the transport of electron neutrinos and antineutrinos. The investigated cases are guided by relativistic double neutron star (NS–NS) and NS–BH merger models, producing ∼3–6 M⊙ BHs with rotation parameters of A
BH ∼ 0.8 and tori of 0.03–0.3 M⊙. Our nucleosynthesis analysis includes the dynamical (prompt) ejecta expelled during the CBM phase and the neutrino and viscously driven outflows of the relic BH–torus systems. While typically ∼20–25 per cent of the initial accretion-torus mass are lost by viscously driven outflows, neutrino-powered winds contribute at most another ∼1 per cent, but neutrino heating enhances the viscous ejecta significantly. Since BH–torus ejecta possess a wide distribution of electron fractions (0.1–0.6) and entropies, they produce heavy elements from A ∼ 80 up to the actinides, with relative contributions of A ≳ 130 nuclei being subdominant and sensitively dependent on BH and torus masses and the exact treatment of shear viscosity. The combined ejecta of CBM and BH–torus phases can reproduce the solar abundances amazingly well for A ≳ 90. Varying contributions of the torus ejecta might account for observed variations of lighter elements with 40 ≤ Z ≤ 56 relative to heavier ones, and a considerable reduction of the prompt ejecta compared to the torus ejecta, e.g. in highly asymmetric NS–BH mergers, might explain the composition of heavy-element deficient stars.
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